Nanolayer CrAlN/TiSiN coating designed for tribological applications

With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H³/E² being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.     

Mechanochemical synthesis of YNbO4:Eu nanocrystalline powder and its structural,microstructural and photoluminescence properties

In this research we prepared nanocrystalline YNbO₄:Eu³⁺ phosphor, i.e. nanophosphor, powder using an efficient mechanochemical method followed by annealing. X-ray diffraction analysis revealed that YNbO₄:Eu³⁺ crystallizes in monoclinic structure C2/c where, from the point of view of A and B in ABO₄ compounds, cation coordination can be noted as [6+2, 4+2]. Crystallite size of about 40 nm, was estimated using Debye Scherrer's equation. Raman spectroscopy with 785 and 532 nm excitation wavelengths is performed to record a majority of materials phonon modes and to provide more in depth understanding of the YNbO₄ structure. Scanning electron microscopy observations indicate that the mechanical treatment during synthesis is causing non-uniformity of the powder microstructure. High resolution photoluminescent measurements upon UV excitation showed intense emission coming from f–f transitions of the europium ion with the lifetime of 0.68 ms, suggesting that the obtained YNbO₄:Eu³⁺ is a good potential phosphor. A comparison of emissive properties with microcrystalline YNbO₄:Eu³⁺ was made and it showed higher values of emission intensity and lifetime of the nanocrystalline sample.     

Fluoride in teas of different types and forms and the exposure of humans to fluoride with tea and diet

Human exposure to the fluoride (F) from commercial teas was assessed. The efficacy of the F leaching was determined from the total F (F_t) contents in the teas (53–435 mg/kg) and the F concentrations in tea infusions (0.31–3.55 mg/l of free F available to human organism). Both were determined with a fluoride ion selective electrode. The efficacies of F leaching from the green, oolong and black teas were 55–90% with continuous, and 74–100% by repeated infusions, and were not affected by the type or the manufactured form. Lower efficacies were observed from Pu’erh teas, 21–38% with continuous, and 37–59% by repeated infusions. The daily intake of F with daily consumption of five cups of tea can represent 9–101% of the adequate intake (AI) for an adult person with 70 kg, and with tea and diet 25–173% of the AI in non-fluoridated and 35–210% of AI in fluoridated areas. The upper limits of these intakes can be already associated with a risk of developing F-related adverse effects.     

On the role of 2,3-dihydro-3,5-dihydroxy-6-methyl-(4<Emphasis Type="Italic">H</Emphasis>)-pyran-4-one in antioxidant capacity of prunes

Despite available reports on phenolic composition and antioxidant capacity (AOC) of fresh plums and prunes, there is a scarcity of published knowledge on the antioxidants formed and/or released during the drying process in the literature. To evaluate the compounds participating in reducing capacity of prunes, we compared aqueous and methanol extracts of fresh plums, commercial prunes and home-made prunes prepared at different drying temperatures using an HPLC method with amperometric detection (HPLC-ECD). The prunes dried at high temperature (90 °C, 18 h) in kitchen or laboratory oven with restricted ventilation gave up to 3.3 times higher electrochemical capacity (EC) than fresh plums (dry matter; P. domestica cv. Domestica) in dependence on production protocol. Drying at 60 °C (low-temperature drying) for 18 h did not change the EC significantly. Yet, lower EC was found in commercial tenderized prunes with sorbate; they were by a factor of 1.1–8.2 lower in EC than the prepared low-temperature prunes. The principle responsible for the increase in EC in the prunes prepared at high temperatures is 2,3-dihydro-3,5-dihydroxy-6-methyl-(4H)-pyran-4-one (DDMP). It was not detected until 74 °C was set during isothermal 18 h drying or until 6 h of drying passed at 90oC drying. The ultimate acceptable dwell-time for the preparation of conveniently eatable prunes dried at 90oC under the conditions used was assessed to 12 h. The EC of plums and prunes as well as the role of DDMP was confirmed by the use of several methods for the assessment of AOC-DPPH^• assay, β-carotene bleaching method, Oxipres test and Schaal oven test.     

Fatigue crack initiation and damage characterization in Brazilian test specimens for adhesive joints

The present study is focused on the fatigue failure initiation at bimaterial corners by means of a configuration based on the Brazilian disc specimens. These specimens were previously used for the generalized fracture toughness determination and prediction of failure in adhesive joints, carried out under static compressive loading. Under static loading, local yielding effects might affect the asymptotic two-dimensional linear elastic stress representation under consideration. Fatigue loading avoids this fact due to the lower load levels used. The present tests were performed using load control; video microscopy and still cameras were used for monitoring initiation and crack growth. The fatigue tests were halted periodically and images of the corner were taken where fatigue damage was anticipated. Damage initiation and subsequent crack growth were observed in some specimens, especially in those which presented brittle failure under static and fatigue tests. These analyses allowed the characterization of damage initiation for a typical bimaterial corner that can be found in composite to aluminium adhesive lap joints.     

Stereometric analysis of nanostructured boehmite coatings synthesized by aluminum nitride powder hydrolysis

We studied the morphological properties of precipitated, nanostructured, boehmite coatings on a polished alumina surface by exploiting the aluminum nitride (AlN) powder hydrolysis at elevated temperatures. The hydrolysis tests of the 3 wt% AlN powder suspensions in the temperature range 50–90 °C were performed in order to estimate the time needed for the synthesis of the coatings. They consisted of interlocked boehmite lamellas, positioned perpendicularly to the ceramic surface, and they exhibited a strong temperature-dependent size and surface density. The aim of this research was a quantitative assessment of the as-formed boehmite coatings. Based on electron microscopy micrographs, a stereometric analysis of the as-prepared coatings was performed in order to estimate the relevant geometric parameters of the lamellas. In spite of the temperature-dependent lamellas’ size and surface density, the specific volume of the coatings was similar for all the synthesis temperatures.     

Discrete (n + 1)-valued states and n-perfect pseudo-effect algebras

We give sufficient and necessary conditions to guarantee that a pseudo-effect algebra admits an (n + 1)-valued discrete state. We introduce n-perfect pseudo-effect algebras as algebras which can be split into n + 1 comparable slices. We prove that the category of strong n-perfect pseudo-effect algebras is categorically equivalent to the category of torsion-free directed partially ordered groups of a special type.     

Signal shaper with a distributed delay: Spectral analysis and design

Input shapers with time delays have proved useful in many applications related to controls for various oscillatory devices, for example flexible manipulators and cranes. In the paper, a novel approach for designing a zero-vibration signal shaper based on equally distributed delay is proposed. The parameter assessment of the shaper is based on the spectral approach. Various characteristics of the shaper are analyzed and compared with the classical zero-vibration shaper with a lumped delay. The analysis shows that the novel shaper is a slower, but more robust alternative to the classical shaper. Besides, the discrete implementation of the shaper is proposed and tested. It includes zero placement based parameter adjustment with the objective to preserve full compensation of the oscillatory mode by the discrete algorithm.